Advanced Technologies of Water and Wastewater Treatment

With more than 2 billion people worldwide suffering from water scarcity, clean water is one of the most important natural resources on earth, whereas wastewater, which corresponds to spent water, can be considered a valuable natural resource if treated and reused. The aim is for this Environments Special Issue on “Advanced Technologies of Water and Wastewater Treatment” to address the most pressing problems of natural water resource contamination, as well as wastewater treatment and reuse. We also aim to present innovative treatment options for aquatic environments.

The main topics of this Special Issue include water and wastewater treatment technologies that can address contaminants of emerging concern for the aquatic environment, such as membrane filtration, adsorption, coagulation, ion exchange, biological processes, ozonation, and advanced oxidation or hybrid processes. Moreover, submissions of papers that deal with the fate and removal of microplastics, heavy metals, pharmaceuticals, oxyanions, toxic dyes, and several other environmental pollutants of global concern, were invited.

Figure 1 illustrates statistical data on the articles published in this Special Issue. A total of seventeen (17) manuscripts were published, of which two (2) were Reviews, one (1) was a Communication, and fourteen (14) were Articles (Figure 1a). As can be seen in Figure 1b, the published articles covered a wide range of applications and topics, with a higher proportion focusing on wastewater treatment and the removal of heavy metals. Specifically, the published papers can be categorized as follows:

• Livestock waste management

In the study by El bied et al., 2024 [1], the impacts of different technologies and approaches were investigated, including the use of Bacillus biological additives (HIPO-PURÍN) and aeration using OXI-FUCH, on GHG (methane (CH₄), carbon dioxide (CO₂), and ammonia (NH₃)) emissions from stored pig slurry. By analyzing the results statistically, the authors demonstrated that the treatment with HIPO-PURÍN achieved significant reductions in CH₄ emissions by 67% and CO₂ emissions by 60%, which were increased to 99% and 87%, respectively, when combined with an aeration system (OXI-FUCH), compared with untreated slurry. Ammonia emissions were substantially reduced by 90% by using biological additives alone and by 76% when combined with aeration. The study was driven by the need to develop sustainable solutions for livestock waste management. In addition, Lamssali et al., 2024 [2], provided valuable insights into optimizing anerobic bioreactor processes for the efficient and environmentally friendly treatment of high-strength wastewaters from swine farms, paving the way to more effective and sustainable management of swine wastewater, which is crucial to meet environmental discharge standards and promoting eco-friendly agricultural practices.

• Drinking Water Treatment Systems

In the study by Aragon et al., 2024 [3], TiO₂-coated meltblown nonwoven fabrics that were prepared via Atomic Layer Deposition (ALD) were applied for the inactivation of Escherichia coli (E. coli). It was observed that in the presence of an ultraviolet light-emitting diode (UV-LED) light source (255 nm), 1.35 log E. coli inactivation was achieved.

• Water Reuse

An interesting review by Florides et al., 2024 [4], investigated the current status of water reuse practices in Europe, delving into various methods of water recovery. This review examined public perceptions and attitudes toward recycled water, offering insights into the societal outlook on this increasingly vital aspect of water management. According to the data presented, the current applications of water reuse in northern Europe are for environmental purposes (51%), while in southern Europe, it is mainly used for irrigation (44%), with Spain reusing the largest volume. In another review from de Campos and Soto, 2024 [5], the authors selected and reviewed articles published in the last six years involving the use of different constructed wetland systems (CWs) and their use alongside other technologies to treat different effluents and in which the quality of different effluents for reuse is discussed. From a total of 81 articles reviewed, 41 presented quantitative data on the quality of the treated effluents in relation to the requirements of reuse regulations in different countries. CWs can be used to treat gray and runoff water, as well as domestic and industrial effluents, with the purpose of reusing them.

• Wastewater Treatment and Reuse

Four (4) commercially available small decentralized technologies (DWWTs) with design capacities of 4–8 PE (population equivalent) were selected and operated with various wastewater compositions in Leipzig, Germany, as presented in the study by Rahman et al., 2024 [6]. The technologies were (i) a moving-bed biofilm reactor (MBBR), (ii) a sequencing batch reactor (SBR), (iii) a membrane bioreactor (MBR), and (iv) an aerated vertical-flow constructed wetland (AVFCW). This study clearly showed that the EU-certified small DWWT technologies can efficiently treat high-strength wastewater with concentrations beyond the EU testing ranges (i.e., BOD₅ > 500 mg/L; COD > 1000 mg/L; TSS > 700 mg/L) and are promising wastewater treatment alternatives for small communities in the rural parts of arid/semi-arid regions. Treating wastewater using small decentralized wastewater treatment (DWWT) technologies in combination with the safe reuse of the treated effluents for agricultural irrigational purposes can potentially create noticeable environmental and economic benefits in arid and semi-arid regions. Plant-wide models for optimizing the operation and maintenance of BTEX (Benzene, toluene, ethylbenzene, and xylenes)-contaminated wastewater treatment and reuse facilities that adhere to the IWA Good Modelling Practice Guidelines were used in the study by Bencsik et al., 2024 [7]. The model-based benchmarking tests of this study demonstrated the applicability of the presented concepts for plant-wide modeling by investigating the impacts of operational parameters of the activated sludge process on the removal efficiency of BTEX chemicals, alongside the demand for granular activated carbon usage in effluent polishing. Moreover, the removal characteristics of high-strength ammonium wastewater using A. faecalis No. 4 were studied and presented by Lee and Joo, 2023 [8], under several operating conditions, such as foam–recycle. Ammonium was first oxidized to hydroxylamine, nitrite, and nitrate under aerobic conditions by A. faecalis No. 4, providing intermediate substrates for subsequent denitrification. Finally, regarding wastewater treatment, a statistical characterization of full-scale thermophilic biological systems was used to inform process optimization by Collivignarelli et al., 2024 [9]. Advanced descriptive statistics (violin graphs) highlighted the treatment effectiveness of this process, which combines thermophilic biodegradation with an ultrafiltration treatment. The authors found that the loading mode of the reactor showed the presence of some peaks, which were uniformly distributed over the different years.

• Pharmaceuticals

Only one paper was submitted to this Special Issue focusing on the removal of pharmaceuticals. Skempi et al., 2023 [10], studied the heterogeneous activation of sodium persulfate (SPS) using nickel oxide/strontium carbonate (NiO/SrCO₃) for the degradation of sulfamethoxazole (SMX), a representative compound from the group of antibiotics. Their results showed that NiO/SrCO₃ exhibited high performance in the activation of SPS, leading to SMX elimination within brief time spans. Overall, the examined system showed promising results for the decomposition of SMX.

• Microplastics

Microplastics are one of the most persistent pollutants affecting the quality of the environment. Thus, in a study included in this Special Issue, conducted by Bule Možar et al., 2023 [11], five bacterial strains (Bacillus cereus, Bacillus licheniformis, Bacillus subtilis, Delftia acidovorans, and Pseudomonas alcaligenes) and five yeast strains (Candida parapsilosis, Geotrichum candidum, Rhodotorula glutinis, Saccharomyces cerevisiae, and Trichosporon sp.) were isolated from environmental samples. Among them, Delftia acidovorans was identified as the bacterium with the highest potential to biodegrade PS and PVC microplastics, while Candida parapsilosis showed the highest potential among the yeasts. The two microorganisms adapted better to the PVC MPs than to the PS MPs and used them as a carbon and energy source. A positive effect of increased cell density and a negative effect of high agitation speed on the biodegradation process were observed.

• Heavy Metal Removal

In their study, Kharel et al., 2023 [12], evaluated the strain of red microalgae Galdieria sulphuraria CCMEE 5587.1 in a controlled laboratory environment for its ability to tolerate and remove two heavy metal (HM) ions, cadmium [Cd(II)] and lead [Pb(II)], in aqueous solutions as a single metal species. The study underscores the dual advantage of G. sulphuraria CCMEE 5587.1, making it a promising candidate for addressing heavy metal pollution in wastewater treatment processes. In addition, Altahaan and Dobslaw, 2024 [13], aimed to quantify the effect of heavy metal inputs resulting from the war on the water and sediment of the Tigris River within the urban area of Mosul, taking seasonal variations (test series from the winter and spring vs. summer and fall) into account and comparing measurement points upstream and downstream of Mosul, and to compare them with existing global limits. Their results demonstrated seasonally independent exceedances of the WHO limit values for Cd, Pb, Cr, and Ni in water and sediments. Moreover, Tolkou and Kyzas, 2023 [14], presented the application of Magnesium/Silica/Lanthamum@Activated Carbon (Mg-Si-La@AC) for the first time in the removal of As(III) from water, resulting in a residual As concentration <10 µg/L.

• Phosphorus Recovery from Wastewater

In the study by Vineyard et al., 2024 [15], BioWin modeling of calprex phosphorus recovery from wastewater was used to predict substantial struvite formation at the Nine Springs Wastewater Treatment plant (Madison, WI, USA), using BioWin 6.2 with modifications to model the acid digestion process. A full-scale CalPrex process was predicted to reduce struvite formation in the anaerobic digesters by 80% and total precipitate formation by 58%. Vineyard et al., 2024, also published another article [16] in this Special Issue, which focused on improving BioWin modeling of phosphorus solubilization in acid-phase digesters.

• Others

In the study by López-Patiño et al., 2023 [17], the main objective was to verify whether it is possible to use a general-pressure hydraulic network analysis program, such as EPANET, for the analysis of the hydraulic performance of siphonic roof drainage systems (SRDSs). SRDSs are an alternative to conventional roof drainage systems (CRDSs) due to the comparative benefits that they offer under fully primed conditions. It was concluded that EPANET is a software that can be used to analyze and, therefore, design siphonic roof drainage systems in buildings.

Figure 1. Statistical data on the published articles: (a) type of publication; (b) topics covered.

Figure 1. Statistical data on the published articles: (a) type of publication; (b) topics covered.

We would like to thank the authors for their contributions and their willingness to share innovative ideas and methods in this Special Issue. In addition, we would like to express our appreciation to the reviewers for the considerable amount of time they invested in providing accurate and fair manuscript evaluations. Finally, we would like to express our pleasure in working with the staff of the Environments Editorial Office on this productive and exciting publication.